Poppers are often used for our warm water fishes here in the US. They float & can imitate many things, such as bait fishes, frogs, small mammals or larger insects. They're not commonly used for trout, but does not mean they can't work.

Most folks cast them, let them sit several seconds, then retrieve with quick, short strips of line. This will make them pop. However, sometimes varying the retrieve cadence & speed is more effective.